Monotonicity Properties of Chemical Reactions with a Single Initial Bimolecular Step

Arbitrary-length reversible chain reactions with a single initial bimolecular step are considered. Monotonicity properties of species concentrations with respect to initial concentrations are determined using the established theory of monotonicity with respect to closed convex cones [1–3]. Strict sign results are obtained.     

The photocurrent response of human cones is fast and monophasic

Background  

The precise form of the light response of human cone photoreceptors in vivo has not been established with certainty. To investigate the response shape we compare the predictions of a recent model of transduction in primate cone photoreceptors with measurements extracted from human cones using the paired-flash electroretinogram method. As a check, we also compare the predictions with previous single-cell measurements of ground squirrel cone responses.     

Polymer crystalline structure and morphology changes in nylon‐6/ZnO nanocomposites

The influence of ZnO nanoparticles on the crystalline structures of nylon‐6 under different crystallization conditions (annealing at different temperatures from the amorphous solid, isothermal crystallization from the melt at different temperatures, and crystallization from the solution) has been examined with differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction, field emission scanning electron microscopy, and Fourier transform infrared. ZnO nanoparticles can induce the γ‐crystalline form in nylon‐6 when it is cooled from the melted state and annealed from the amorphous solid. This effect of ZnO nanoparticles increases with decreasing particle size and changes under different crystallization conditions. The effects of ZnO nanoparticles on the crystallization kinetics of nylon‐6 have also been studied with DSC. The results show that ZnO nanoparticles have two competing effects on the crystallization of nylon‐6: inducing the nucleation but retarding the mobility of polymer chains. Finally, the melting behavior of the composites has been investigated with DSC, and the multiple melting peaks of composites containing ZnO nanoparticles and pure nylon‐6 are ascribed to the reorganization of imperfect crystals. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1033–1050, 2003     

Extended Corannulenes: Aromatic Bowl/Sheet Hybridization

Among sheet/sheet polynuclear aromatic hydrocarbon (PAH) hybrids, a buckybowl–graphene hybrid has been used as a model to explore the effects of physical properties of PAHs with distinct planar and bowl regions. Activation of a C(Ar)? F bond was used to synthesize this corannulene/graphenic hybrid. Photophysical and voltammetric studies together with high‐level computations revealed curvature and extended π‐effects on the properties of these materials.     

Radioaktive Referenzpräparate

Es wird über Methoden der Entwicklung und Herstellung von radioaktiven Referenzpräparaten berichtet, eine Reihe dieser Präparate schwer punktmäβig dargestellt und ihre Anwendung erläutert.     

ACCELERATED OPTIMIZATION WITH ORTHOGONALITY CONSTRAINTS

We develop a generalization of Nesterov’s accelerated gradient descent method which is designed to deal with orthogonality constraints.To demonstrate the effectiveness of our method,we perform numerical experiments which demonstrate that the number of iterations scales with the square root of the condition number,and also compare with existing state-of-the-art quasi-Newton methods on the Stiefel manifold.Our experiments show that our method outperforms existing state-of-the-art quasi-Newton methods on some large,ill-conditioned problems.     

Determination of Two Donor (Majority) Levels in Semiconductors from Hall Effect Measurements

Temperature dependence of the carrier concentration n₀ is calculated for different impurity parameters under the assumption that two donor (majority) levels are present in a semiconductor. A nonlinear least squares fit using an equation cubic in n₀ yields the impurity parameters of both impurities with relatively small errors. This determination of impurity parameters is suitable also in the case of donor (majority) levels with similar ionization energies. Through that it is possible semiconductors with two majority levels to analyse by Hall effect measurements. In the case of clearly different donor (majority) activation energies the cubic equation can be approximated by two quadratic relations in n₀ valid in the high and low temperature region, respectively.